There will be more itching, sneezing, swelling and gasping for breath as Pennsylvania’s climate shifts and residents are exposed to more poison ivy, stinging insects, pollen allergies and lyme-disease-bearing ticks, and experience increased asthma, respiratory disease and heat-related deaths.

That was the assessment of scientists and physicians at a one-day climate change conference sponsored by the Allegheny County Health Department and the University of Pittsburgh’s Graduate School of Public Health last week.

They said a silver lining is that Pennsylvanians won’t see the worst of those negative impacts until after 2050. But the bad news, echoing the findings contained in the third U.S. National Climate Assessment released May 6, is that the changes already have begun.

And, they agreed, the negative consequences of climate change brought on by man-made emissions of greenhouse gases will worsen the longer the world waits to reduce those emissions.

Raymond Najjar, a professor of oceanography in the Meteorology Department at Penn State University and an author of the 2009 Pennsylvania Climate Impact Assessment, said the most recent assessment released three weeks ago shows “some climate change is unavoidable,” and the state will get warmer and wetter. Heavy downpours will be more intense and more frequent.

He predicted that unless Pennsylvania cuts its emissions of greenhouse gases — including nitrogen oxides, carbon dioxide, sulfur dioxide and volatile organic compounds — to 20 percent of what they are now, the state’s summer heat index will become 8 to 10 degrees warmer by the end of this century.

Without that level of emissions cuts, the number of days the temperature tops 90 degrees Fahrenheit each year will increase from 10 to 65 and Pennsylvania’s climate will resemble what is found now in northern Alabama.

“Pennsylvania has not done enough to reduce emissions and support renewable energy sources,” said Mr. Najjar, adding that even if emissions are reduced by 80 percent, Pennsylvania likely will see summer temperatures rise by 5 degrees Fahrenheit, giving it a climate resembling that of southern Kentucky today.

City and county officials must start now to adapt policies and programs to climate-altered and expanding public health needs, said Karen Hacker, Allegheny County Health Department director.

“Infectious diseases, ticks, mosquitoes will all increase as the climate warms, as will severity and incidence of asthma, water problems and severe weather,” Dr. Hacker said. “The increases will likely be incremental, but the impacts will collectively be bigger.”

Leonard Bielory, a professor at Rutgers University where he is studying the impact of a warming climate on allergies, said globally longer pollination seasons are expected to increase the duration of exposure and also the number of individuals who develop sensitivity to it.

“Ragweed is responding to climate change on a continental basis, so we’re seeing earlier and later pollen seasons and it moves northward with warmer climate,” he said. “By 2020, we expect to see pollen increase by 20 percent in Pennsylvania, and by 2050 sensitivity to allergens could double from what it is now.”

Dr. Bielory said research shows climate change is also likely to cause an increase in dust mites, stinging insects and cockroaches. The production of poison ivy oil, which causes the itchy skin rash, will increase as carbon dioxide levels rise, weed growth will be stimulated and peanut allergies, which have doubled in each of the last several decades, will continue to increase.

Lyme disease, the most prevalent vector-borne disease in the U.S. with 30,000 diagnosed and perhaps nine times more undiagnosed cases, also is likely to increase among humans as the geographic range of the tick that causes it continues to expand, according to Dustin Brisson, an associate professor of biology at the University of Pennsylvania, whose research involves evolutionary biology, molecular genetics and microbial ecology.

Peter Adams, a professor of civil and environmental engineering and engineering and public policy at Carnegie Mellon University, said warmer air temperatures combined with expected higher humidity “makes the atmosphere more able to do chemistry and produce compounds that could impact human health.”

One of those compounds likely to increase is ground-level ozone, the primary component of unhealthy smog. Methane emissions from increased shale gas drilling, along with nitrogen oxides and volatile organic compound emissions from drilling operations and increased truck traffic, also could rise.

“Depending on how tightly those [shale gas drilling] operations are controlled,” Mr. Adams said, “there could be significant health impacts on Pittsburgh and Philadelphia and even more significantly in the center of the state.”

Clifford Mitchell, director of the Maryland Department of Health and Mental Hygiene, said that mitigation policies are important and the public needs to get involved to force emissions reductions, but health officials need to plan now for how a changing climate will impact local populations and communities.

“We need to help people adapt,” Dr. Mitchell said. “We’re going to be doing damage control and we need to figure out how to do that systematically.”